I'm with Wally on this one. There are to many variables involved in a safe landing or launch too have a hard and fast rule about it.
 I was always the stern guy, my bow guy was half my size. On some landings that didn't allow me to exist safely, I would have him get out, and turn and straddle the bow using his body weight and arms to stabilize the canoe.
I would either climb out a side, OR in some cases, crawled forward over the packs until I had a safe place to exit.
 Used the same tactic in reverse sometimes. Wasn't pretty, but we never dumped and that's all that matters ;)